The idea is based on when someone purchase a product from your sellix site he needs to input his email adress well wont it be a good idea to have a email panel from sellix to send to your customer an email about news, discounts or special offers? By just few clicks? So you will save time taking email per email and sending it manually by this you will just select send email to all who clicked on checkbox "Subscribe to newsletter". I think it will be a good way let you customers know about news!